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Synthesis of superheavy elements at the Dubna gas-filled recoil separator
A survey of experiments at the Dubna gas-filled recoil separator (Laboratory of Nuclear Reactions, JINR, Dubna) aimed at the detection and study of the “island of stability” of superheavy nuclei produced in complete fusion reactions of {sup 48}Ca ions and {sup 238}U–{sup 249}Cf target nuclei is given. The problems of synthesis of superheavy nuclei, methods for their identification, and investigation of their decay properties, including the results of recent experiments at other separators (SHIP, BGS, TASCA) and chemical setups, are discussed. The studied properties of the new nuclei, the isotopes of elements 112–118, as well as the properties of their decay products, indicate substantial growth of stability of the heaviest nuclei with increasing number of neutrons in the nucleus as the magic number of neutrons N = 184 is approached.
DGFRS-2—A gas-filled recoil separator for the Dubna Super Heavy Element Factory
The main goal of development of the new Dubna Gas-Filled Recoil Separator (DGFRS-2) is to sufficiently improve the efficiency of studies on heavy and superheavy nuclei at the Super Heavy Element Factory of the Flerov Laboratory of Nuclear Reactions (FLNR) at the Joint Institute for Nuclear Research. The use of beams with the intensity up to 6×10 13 s -1 (10 pμA) delivered by the DC280 cyclotron requires an effective setup providing high suppression of background reaction products. Additionally, the described gas-filled separator is optimized for synthesis and study of heavy isotopes produced in complete fusion reactions of massive nuclei. Basic characteristics of DGFRS-2, as well as the results of the first test experiments, are presented. In comparison to the DGFRS-1, the transmission efficiency was doubled, and the background was reduced by a factor 200.
Synthesis of new superheavy elements using the Dubna Gas-Filled Separator: The complex of technologies
All the new isotopes of superheavy elements in the reactions with {sup 48}Ca ions and actinide targets, synthesized at the Flerov Laboratory of Nuclear Reactions (FLNR), have been obtained at the Dubna Gas-Filled Recoil Separator (DGFRS). Success was achieved with the use of several techniques, algorithms and approaches with record performance in their area. The most sophisticated of them are rare event detection technology, methods of measuring the effective equilibrium charges of heavy ions and nuclei in hydrogen at low pressure, modified approaches to evaluation of probabilistic characteristics of detected multichain events, beam-free test methods of detection equipment, and some other ones. The author analyzes the approaches that have led ultimately to a real breakthrough and an advance in experiments on the synthesis of superheavy elements. The development of detection systems also attracts the authors’ attention. Contributions from some facilities—such as SHIP, TASCA, and GARIS (RIKEN)—to synthesis experiments are partially noted. Under consideration are methods of automation of similar experiments, including the development of control and shielding systems for operation with highly active actinide targets. Some techniques for detecting α decay of heavy nuclei that came before the current experiments with electromagnetic separators are reviewed briefly. The methods, algorithms and hardware presented cover a more than twenty-year period of commissioning and application in long-term experiments at FLNR DGFRS.
Automation of experiments at Dubna Gas-Filled Recoil Separator
Approaches to solving the problems of automation of basic processes in long-term experiments in heavy ion beams of the Dubna Gas-Filled Recoil Separator (DGFRS) facility are considered. Approaches in the field of spectrometry, both of rare α decays of superheavy nuclei and those for constructing monitoring systems to provide accident-free experiment running with highly radioactive targets and recording basic parameters of experiment, are described. The specific features of Double Side Silicon Strip Detectors (DSSSDs) are considered, special attention is paid to the role of boundary effects of neighboring p–n transitions in the “active correlations” method. An example of an off–beam experiment attempting to observe Zeno effect is briefly considered. Basic examples for nuclear reactions of complete fusion at {sup 48}Ca ion beams of U-400 cyclotron (LNR, JINR) are given. A scenario of development of the “active correlations” method for the case of very high intensity beams of heavy ions at promising accelerators of LNR, JINR, is presented.
Nuclear Data Sheets for A=266,270,274,278,282,286,290,294,298☆
Spectroscopic information such as production, identification, half-lives, decay modes and possible excited states for experimentally known nuclides of mass numbers 266, 270, 274, 278, 282, 286, 290, 294, and 298 are presented together with the recommended values, superseding information and data in the previous ENSDF and NDS evaluation by 2005Gu33. No nuclides have yet been identified for A=302. In the last 14 years, large amounts of new and definitive data on the superheavy nuclides (SHN) have become available, thus changing almost entirely the landscape of nuclear data in this mass region, as also indicated by a number of recent review articles: 2017Og01, 2016Ho09, 2016Ho06 (for fission barriers), 2015Og05, 2015Og07, 2015Mo25, 2015OgZX, 2013Th02, and 2011Og07. See 2016Ka49 for IUPAC technical discussions for the discovery of Z=117 (Ts), Z=115 (Mc), Z=113 (Nh), 2001Ka70 and 2003Ka71 for Z=110-112, 2011Ba54 for Z≥113, 2009Ba62 for Z=112, and 2016Ka50 for Z=118 (Og). A special issue of Nuclear Physics A444 (2015) is devoted to research on superheavy elements (SHE) with 27 articles. In particular, see article by 2015Ko20 on mass spectrometric searches for superheavy elements in terrestrial matter. See also Proceedings of Nobel Symposium NS160 ‘Chemistry and Physics of Heavy and Superheavy Elements’ published in Eur. Phys. Jour. Web of Conferences 131 (2016), in particular 2016UtZZ, 2016DmZZ and 2016HoZY. See also 2016DuZX for future prospects of discovery of elements beyond Z=118 A=266: {sup 266}Db, {sup 266}Sg, {sup 266}Bh, {sup 266}Hs and {sup 266}Mt are the experimentally identified nuclides with A=266. Identification of {sup 266}Lr from α decay of {sup 270}Db has been proposed by 2014Kh04 from experiments at GSI, but complete details and analyses of all the four decay chains reported in this experiment have not yet been published, and discussion in 2015Og05 review article considering their work from Dubna (2013Og04, 2011Og04) and from GSI (2014Kh04) still concluded that {sup 270}Db decayed dominantly by SF mode, in contrast with dominant α decay mode proposed by 2014Kh04. Experiments carried out at FLNR-JINR-Dubna in collaboration with LLNL and ORNL, GSI-SHIP facility, RIKEN, and LBNL facilities: {sup 266}Db from the α-decay of {sup 282}Nh in two correlated decay chains at Dubna; {sup 266}Sg as α-daughter of {sup 270}Hs in 12 correlated decay chains at Dubna and GSI; {sup 266}Bh in α decay of {sup 278}Nh in three correlated decay chains observed at RIKEN, and also directly with one event in {sup 249}Bk({sup 22}Ne,5n) at LBNL, and with four events in {sup 243}Am({sup 26}Mg,3n) at HIRFL-Lanzhou; {sup 266}Hs as α-daughter of {sup 270}Ds at GSI in two different experiments, six correlated decays in the first, and 25 decay chains in the second experiment, the analysis of which has not been fully reported as yet; and {sup 266}Mt directly in {sup 209}Bi({sup 58}Fe,n) reaction at GSI in two different experiments, observing three events in the first experiment and 12 events in the second, also produced in {sup 208}Pb({sup 59}Co,n) reaction at LBNL, observing five correlated decay chains. See also 2000Ho27 for discussion on {sup 266}Sg and {sup 266}Mt. A=270: {sup 270}Db, {sup 270}Bh, {sup 270}Hs, {sup 270}Mt and {sup 270}Ds are the experimentally identified nuclides with A=270 are presented. Experiments carried out at FLNR-JINR-Dubna in collaboration with LLNL and ORNL, GSI-SHIP facility, and RIKEN: {sup 270}Db from the decay of {sup 294}Ts in six correlated decay chains at Dubna and GSI; {sup 270}Bh as α great-granddaughter of {sup 282}Nh in two correlated decay chains observed at Dubna; {sup 270}Hs directly in {sup 248}Cm({sup 26}Mg,4n) reaction at GSI, and in {sup 226}Ra({sup 48}Ca,4n) reaction at Dubna; {sup 270}Mt as granddaughter of {sup 278}Ts in three correlated decay chains at RIKEN; and {sup 270}Ds directly in {sup 207}Pb({sup 64}Ni,n) at GSI in 33 correlated decay chains. A=274: {sup 274}Bh, {sup 274}Mt and {sup 274}Rg are the experimentally identified nuclides with A=274. Search for {sup 274}Ds in {sup 238}U({sup 40}Ar, 4n),E=5.7 MeV/nucleon reaction and subsequent α decays at GSI (1990Sc11) proved negative. Experiments carried out at FLNR-JINR-Dubna in collaboration with LLNL and ORNL, GSI-SHIP facility, and RIKEN: {sup 274}Bh from the decay of {sup 294}Ts in six correlated decay chains at Dubna and GSI, {sup 274}Mt produced as α daughter of {sup 282}Nh in two correlated decay chains observed at Dubna, and {sup 274}Rg as α daughter of {sup 278}Nh produced in three correlated decay chains at RIKEN. A=278: {sup 278}Mt, {sup 278}Rg and {sup 278}Nh are the experimentally identified nuclides with A=278. A very tentative evidence is provided for {sup 278}Bh and {sup 278}Hs from a chain originally observed and assigned to {sup 289}Fl by 1999Og10, but later reassigned by 2004Og10 to {sup 290}Fl, and further discussed in detail by 2016Ho09, where, based on systematics of α decays and SF half-lives, {sup 290}Fl is proposed to decay via ε mode to {sup 290}Nh, which then decays by an α chain, ending in {sup 278}Bh that decays by SF mode. Experiments carried out at FLNR-JINR-Dubna in collaboration with LLNL and ORNL labs in the USA, GSI-SHIP facility, and RIKEN: {sup 278}Mt from the decay of {sup 294}Ts in six correlated decay chains at Dubna and GSI, {sup 278}Rg produced as α daughter of {sup 282}Nh in two correlated decay chains observed at Dubna, and {sup 278}Nh produced directly in three correlated decay chains at RIKEN. A=282: {sup 282}Rg, {sup 282}Cn and {sup 282}Nh are the experimentally identified nuclides with A=282. A very tentative evidence is provided for {sup 282}Mt and {sup 282}Ds from a chain originally observed and assigned to {sup 289}Fl by 1999Og10, but later reassigned by 2004Og10 to {sup 290}Fl, and further discussed in detail by 2016Ho09, where, based on systematics of α decays and SF half-lives, {sup 290}Fl is proposed to decay via ε mode to {sup 290}Nh, which then decays by an α chain, ending in {sup 278}Bh that decays by SF mode. Experiments carried out at FLNR-Dubna, in collaboration with LLNL and ORNL labs in the USA, and at GSI-SHIP facility confirm the identification of these isotopes, {sup 282}Rg in α decay chain of {sup 294}Ts in six correlated decay chains at Dubna and GSI, {sup 282}Cn produced in four ways at Dubna: independently in one correlated decay chain, as α daughter of {sup 286}Lv in 11 correlated decay chains, as α grand-daughter of {sup 290}Lv in 12 correlated decay chains, as α great-grand daughter of {sup 294}Og in four correlated decay chains, and {sup 282}Nh produced at Dubna directly in two correlated decay chains. A=286: {sup 286}Nh and {sup 286}Fl are the only experimentally identified nuclides with A=286. A very tentative evidence is provided for {sup 286}Rg and {sup 286}Cn from a chain originally observed and assigned to {sup 289}Fl by 1999Og10, but later reassigned by 2004Og10 to {sup 290}Fl, and further discussed in detail by 2016Ho09, where, based on systematics of α decays and SF half-lives, {sup 290}Fl is proposed to decay via ε mode to {sup 290}Nh, which then decays by an α chain, ending in {sup 278}Bh that decays by SF mode. 2017Ka66 in experiments at RIKEN using GARIS separator interpret one correlated decay chain in three different ways, one involving possible production of {sup 294}Lv in {sup 248}Cm({sup 48}Ca,2n),E=261.6 MeV, and α decay to {sup 290}Fl which further decays to {sup 286}Cn. Experiments carried out at FLNR-Dubna, in collaboration with LLNL and ORNL labs in the USA, and at GSI-SHIP facility confirm the identification of these isotopes, {sup 286}Nh as α grand-daughter of {sup 294}Ts in six correlated decay chains, and {sup 286}Fl produced in three ways: independently in 11 correlated decay chains, as α daughter of {sup 290}Lv in 12 correlated decay chains, and as α grand-daughter of {sup 294}Og in four correlated decay chains. A=290: {sup 290}Mc and {sup 290}Lv are the only experimentally identified nuclides with A=290. A tentative evidence is provided for {sup 290}Nh and {sup 290}Fl from a chain originally observed and assigned to {sup 289}Fl by 1999Og10, but later reassigned by 2004Og10 to {sup 290}Fl, and further discussed in detail by 2016Ho09, where, based on systematics of α decays and SF half-lives, {sup 290}Fl is proposed to decay via ε mode to {sup 290}Nh, which then decays by an α chain, ending in {sup 278}Bh that decays by SF mode. 2017Ka66 in experiments at RIKEN using GARIS separator interpret one correlated decay chain in three different ways, one involving possible production of {sup 294}Lv in {sup 248}Cm({sup 48}Ca,2n),E=261.6 MeV, and α decay to {sup 290}Fl. Experiments carried out at FLNR-Dubna, in collaboration with LLNL and ORNL labs in the USA, and at GSI-SHIP facility confirm the identification of these isotopes, {sup 290}Mc as α daughter of {sup 294}Ts in six correlated decay chains, and {sup 290}Lv produced in two ways, independently in 14 correlated decay chains, and as α daughter of {sup 294}Og in four correlated decay chains. A=294: {sup 294}Ts and {sup 294}Og are the only experimentally identified nuclides with A=294. Experiments carried out at FLNR-Dubna, in collaboration with LLNL and ORNL labs in the USA, and at GSI-SHIP facility confirm the identification of these isotopes, with a total of six EVR-α-SF correlated decay chains observed for {sup 294}Ts and four for {sup 294}Og. Tentative identification of {sup 294}Lv is provided by 2017Ka66 from the observation one correlated event using GARIS-RIKEN facility, where this event is interpreted in three possible ways, two interpretations lead to production of {sup 293}Lv and successive odd-A nuclides of {sup 289}Fl, {sup 285}Cn and {sup 281}Ds, whereas the third prediction starts with the production of {sup 294}Lv and successive {sup 290}Fl and {sup 286}Cn nuclides. Search for {sup 294}Rg in natural gold materials (2011De03), and for {sup 294}Ds, {sup 294}Fl and {sup 294}Mc in natural Pt, Pb and Bi samples (2011De21) using accelerator mass spectroscopy (AMS) proved negative, with extremely low upper limits established. Also 1980St05 did not see any evidence for {sup 294}Ds in natural Pt sample using AMS. A=298: Search for {sup 298}120 through fusion-evaporation reaction at Dubna, and for {sup 298}Fl and {sup 298}Mc in natural Pt, Pb and Bi samples using accelerator mass spectroscopy (AMS) proved negative. Tentative assignment of three α-α-α decay chains by 2016Ho09 to {sup 299}120 in {sup 248}Cm({sup 54}Cr,3n){sup 299}120 at GSI was refuted by 2017He11, assigning these correlations to random events, instead. A=302: Fluorescent x rays from Z=120 element were observed by 2012Fr03 from compound nucleus {sup 302}120 produced in {sup 238}U({sup 64}Ni,X),E=6.6 MeV/nucleon at GANIL, and x-ray yields were measured, together with minimum average time deduced from x-ray multiplicity. The compound nucleus could decay by 3n- or 4n-channels to produce {sup 299}120 or {sup 298}120. 2012He05 and 2016Ho09 also produced {sup 302}120 compound nucleus in {sup 248}Cm({sup 54}Cr, xn){sup 302}120{sup *},E=6.035 MeV/nucleon; and {sup 238}U({sup 64}Ni,xn){sup 302}120{sup *},E=5.53 MeV/nucleon reactions using UNILAC at GSI. Three α-α-α correlated decays from {sup 248}Cm({sup 54}Cr,xn){sup 302}120{sup *} reaction were tentatively assigned by 2016Ho09 to {sup 299}120 decay, however, a detailed analysis by 2017He11 refuted this claim, ascribing these events to random sequences. There are no data tables for A=302.
Geometry and harmonic superspace: Some recent progress
This contribution follows the talk, given by F. Delduc at the conference SQS’2011 in Dubna, Russia (July 18–23, 2011). To a considerable extent it is a summary of known facts about the links between geometry and extended supersymmetry in d = 1 mechanics, with emphasis on the harmonic superspace method created in Dubna in the 80’s. Some recent developments based on [1] are also presented.
E-36: The First Proto-Megascience Experiment at NAL
E-36, an experiment on small-angle proton-proton scattering, began testing equipment at the National Accelerator Laboratory (NAL) using a newly achieved 100 GeV proton beam on February 12, 1972, marking the beginning of NAL’s experimental program. This experiment, which drew collaborators from NAL, the Joint Institute for Nuclear Research (Dubna, USSR), the University of Rochester (Rochester, New York), and Rockefeller University (New York, New York) was significant not only as a milestone in Fermilab’s history but also as a model of cooperation between the East and West at a time when Cold War tensions still ran high. An examination of the origin, operation, and resolution of E-36 and the chain of experiments it spawned reveals the complex interplay of science and politics that drove these experiments as well as seeds of the megascience paradigm that has come to dominate high energy physics research since the 1970s.
Recoil-α-fission and recoil-α–α-fission events observed in the reaction 48 Ca + 243 Am
Here, products of the fusion-evaporation reaction 48 Ca+ 243 Am were studied at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany. Amongst the detected thirty correlated α-decay chains associated with the production of element Z=115, two recoil-α-fission and five recoil-α–α-fission events were observed. The latter five chains are similar to four such events reported from experiments performed at the Dubna gas-filled separator, and three such events reported from an experiment at the Berkeley gas-filled separator. The four chains observed at the Dubna gas-filled separator were assigned to start from the 2 n -evaporation channel 289 115 due to the fact that these recoil-α–α-fission events were observed only at low excitation energies. Contrary to this interpretation, we suggest that some of these recoil-α–α-fission decay chains, as well as some of the recoil-α–α-fission and recoil-α-fission decay chains reported from Berkeley and in this article, start from the 3 n -evaporation channel 288 115.
Experiments on the synthesis of superheavy nuclei Fl 284 and Fl 285 in the Pu 239 , 240 + Ca 48 reactions
Irradiations of 239 Pu and 240 Pu targets with 48Ca beams aimed at the synthesis of Z=114 flerovium isotopes were performed at the Dubna Gas Filled Recoil Separator. A new spontaneously fissioning (SF) isotope 284 Fl was produced for the first time in the 240 Pu+ 48 Ca (250 MeV) and 239 Pu+ 48 Ca (245 MeV) reactions. The cross section of the 239 Pu( 48 Ca,3n) 284 Fl reaction channel was about 20 times lower than predicted by theoretical models and about 50 times lower than the maximum fusion-evaporation cross section for the 3n and 4n channels measured in the 244 Pu+ 48 Ca reaction. In the 240 Pu+ 48 Ca experiment, performed at 245 MeV in order to maximize the 3n-evaporation channel, three decay chains of 285 Fl were detected. The α-decay energy of 285 Fl was measured for the first time and decay properties of its descendants 281 Cn, 277 Ds, 273 Hs, 269 Sg, and 265 Rf were determined with higher accuracy. The assignment of SF events observed during the irradiation of the 240 Pu target with a 250 MeV 48 Ca beam to 284 Fl decay is presented and discussed. The cross sections at both 48 Ca energies are similar and exceed that observed in the reaction with the lighter isotope 239 Pu by a factor of 10. In conclusion, the decay properties of the synthesized nuclei and their production cross sections indicate a rapid decrease of stability of superheavy nuclei as the neutron number decreases from the predicted magic neutron number N = 184.
Measurement of analyzing power for the reaction p-vector +CH{sub 2} at polarized proton momentum of 7.5 GeV/c (ALPOM2 proposal)
An accurate data base for the analyzing power of thick CH{sub 2} analyzers for high energy protons has been at the basis of several research efforts in a number of laboratories. Starting in the late eighties such data were collected at SATURNE in Saclay, and with the Synchrophasotron in Dubna, and led to an extensive program of study of polarization phenomena in pd interaction, either backward elastic scattering or breakup [1–6]. At about the same time it became evident that measuring polarization observables in elastic ep was going to be the best approach to determine the form factors of the proton, G {sub Ep }and G {sub Mp }, as had been predicted by Akhiezer and Rekalo [7].
Dynamics of Charge States of Relativistic Gold Ion Beams Passing through Cu and Au Foils in the NICA Project
In order to study the properties of dense baryonic matter, an accelerator complex is under development at the Joint Institute for Nuclear Research (Dubna, Russia) within the new NICA project. The NICA project assumes the use of accelerated ion beams ranging from protons to gold ions with relativistic energies up to 4.5 GeV/nucleon. To design experiments, it is necessary to have information on the efficiency of the yield of bare gold nuclei formed at the passage of a gold ion beam with energies of about several hundreds of MeV per nucleon through a foil of a specialized stripping station at the output of the booster of the accelerator. In this work, the optimal conditions (material and thickness of the foil and the energy of the ion) for the formation of fractions of bare gold nuclei with a probability of 80–90% have been determined by calculating electron loss and capture cross sections, as well as the dynamics of charge states of gold ions colliding with copper and gold foils at energies of 400 and 600 MeV/nucleon,.
Nuclear-nuclear collision centrality determination by the spectators calorimeter for the MPD setup at the NICA facility
The work conditions of the hadron calorimeter for spectators registration (Zero Degree Calorimeter, ZDC) were studied for the heavy nuclei collisions with the several GeV invariant energy. The ZDC simulations were performed for the MPD (Multi-Purpose Detector) at the NICA (Nuclotron-based Ion Collider fAcility) collider, which are under developement at the Joint Institute for Nuclear Research (JINR, Dubna). Taking into account the spectator nuclear fragments leads to a nonmonotonic dependence of the ZDC response on the impact parameter. The reason for this dependence studied with several event generators is the primary beam hole in the ZDC center. It is shown, that the ZDC signal should be combined with a data from other MPD-NICA detector subsystems to determine centrality.
Rapidity distributions of hadrons in the HydHSD hybrid model
A multistage hybrid model intended for describing heavy-ion interactions in the energy region of the NICA collider under construction in Dubna is proposed. The model combines the initial, fast, interaction stage described by the model of hadron string dynamics (HSD) and the subsequent evolution that the expanding system formed at the first stage experiences at the second stage and which one treats on the basis of ideal hydrodynamics; after the completion of the second stage, the particles involved may still undergo rescattering (third interaction stage). The model admits three freeze-out scenarios: isochronous, isothermal, and isoenergetic. Generally, the HydHSD hybrid model developed in the present study provides fairly good agreement with available experimental data on proton rapidity spectra. It is shown that, within this hybrid model, the two-humped structure of proton rapidity distributions can be obtained either by increasing the freeze-out temperature and energy density or by more lately going over to the hydrodynamic stage. Although the proposed hybrid model reproduces rapidity spectra of protons, it is unable to describe rapidity distributions of pions, systematically underestimating their yield. It is necessary to refine the model by including viscosity effects at the hydrodynamic stage of evolution of the system and by considering in more detail the third interaction stage.
Experimental setup for ground-based measurements in preparing cosmic experiments to study nuclear planetology
An experimental laboratory setup combining various gamma spectrometers and neutron generators that is intended for operating at the experimental nuclear-planetology facility deployed at the Joint Institute for Nuclear Research (Dubna, Russia) in order to perform physical calibrations of active gamma and neutron spectrometers is described.
Walls of Nonlinear Sigma Models on SO(2N)/U(N) with N > 3
We study walls of mass-deformed Kähler nonlinear sigma models on SO(2N)/ U(N). This article is prepared for the proceedings of International Workshop “Supersymmetries and Quantum Symmetries—SQS’2017”, which was held in Bogoliubov Laboratory of Theoretical Physics, JINR, Dubna from 31 July to 5 August, 2017. The talk was based on [1].
Hadron Physics at the Charm and Bottom Thresholds and Other Novel QCD Physics Topics at the NICA Accelerator Facility
The NICA collider project at the Joint Institute for Nuclear Research in Dubna will have the capability of colliding protons, polarized deuterons, and nuclei at an effective nucleon-nucleon center-of mass energy in the range {radical}s{sub NN} = 4 to 11 GeV. I briefly survey a number of novel hadron physics processes which can be investigated at the NICA collider. The topics include the formation of exotic heavy quark resonances near the charm and bottom thresholds, intrinsic strangeness, charm, and bottom phenomena, hidden-color degrees of freedom in nuclei, color transparency, single-spin asymmetries, the RHIC baryon anomaly, and non-universal antishadowing.
Californium Electrodepositions at Oak Ridge National Laboratory
Electrodepositions of californium isotopes were successfully performed at Oak Ridge National Laboratory (ORNL) during the past year involving two different types of deposition solutions, ammonium acetate (NH 4 C 2 H 3 O 2 ) and isobutanol ((CH 3 ) 2 CHCH 2 OH). A californium product that was decay enriched in 251 Cf was recovered for use in super-heavy element (SHE) research. This neutron-rich isotope, 251 Cf, provides target material for SHE research for the potential discovery of heavier isotopes of Z=118. The californium material was recovered from aged 252 Cf neutron sources in storage at ORNL. These sources have decayed for over 30 years, thus providing material with a very high 251 Cf-to- 252 Cf ratio. After the source capsules were opened, the californium was purified and then electrodeposited using the isobutanol method onto thin titanium foils for use in an accelerator at the Joint Institute for Nuclear Research in Dubna, Russia. Another deposition method, ammonium acetate, was used to produce a deposition containing 1.7 0.1 Ci of 252 Cf onto a stainless steel substrate. This was the largest single electrodeposition of 252 Cf ever prepared. The 252 Cf material was initially purified using traditional ion exchange media, such as AG50-AHIB and AG50-HCl, and further purified using a TEVA-NH 4 SCN system to remove any lanthanides, resulting in the recovery of 3.6 0.1 mg of purified 252 Cf. The ammonium acetate deposition was run with a current of 1.0 amp, resulting in a 91.5% deposition yield. Purification and handling of the highly radioactive californium material created additional challenges in the production of these sources.